As part of an effort to build a prototype flow battery system using a nano-suspension containing β-Ni(OH) nanoparticles as the cathode material, nano-sized β-Ni(OH) particles with well-controlled particle size and morphology were synthesized via the one-step precipitation of a NiCl precursor. The composition and morphology of the nanoparticles were characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The XRD patterns confirmed that β-Ni(OH) was successfully synthesized, while SEM results showed that the particle sizes range from 70 to 150 nm. To ensure that Ni(OH) could be employed in the nano-suspension flow battery, the electrochemical performance of the synthesized β-Ni(OH) was initially tested in pouch cells through charge/discharge cycling. The phase transformations occurring during charge/discharge were investigated using X-ray absorption spectroscopy to obtain the shift in the oxidation state of Ni (X-ray adsorption near edge structure, XANES) and the distances between Ni and surrounding atoms in charged and discharged states (extended X-ray absorption fine structure, EXAFS). XANES results indicated that the electrode in the discharged state was a mixture of phases because the edge position did not shift back completely. XAFS results further proved that the discharge capacity was provided by β-NiOOH and the ratio between β-Ni(OH) and g-NiOOH in the electrode in the discharged state was 71:29. Preliminary nano-suspension tests in a lab-scale cell were conducted to understand the behavior of the nano-suspension during charge/discharge cycling and to optimize the operating conditions.